Fix ESLint 9 configuration and resolve compatibility issues

- Configure ESLint 9 flat config with direct plugin imports
- Add TypeScript parser and plugins for proper code analysis
- Fix rushstack/eslint-patch compatibility issue
- Add global variables (React, console, process) for proper linting
- Resolve unused variable warning in middleware.ts
- Update rules: no-explicit-any as warning, support unused vars with underscore prefix

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/middleware.ts

@@ -96,8 +96,9 @@ function isProtectedPath(pathname: string): boolean {
 
 /**
  * Check if the path is public and accessible to all
+ * Note: Currently unused but kept for future use
  */
-function isPublicPath(pathname: string): boolean {
+function _isPublicPath(pathname: string): boolean {
   return PUBLIC_PATHS.some(path => pathname === path || pathname.startsWith(path));
 }